Method and apparatus for cleaning exhaust gases from oxygen steelmaking furnaces



April 25, 1967 1 D MARlNQ Y 3,315,443

METHOD AND APPARATUS FOR CLEANING EXHAUST GASES FROM OXYGEN STEELMAKING FURNACES Filed 0G13. 5, 1965 I. l. fl .Fxf

Attorney //v VEA/Tof? JESSE 0. MAR/N0 mm .hl II Y fwn @Ww/GM [l 'Hill |||I j? G lv Mv t United States Patent O Ware Filed Oct. 5, 1965, Ser. No. 493,149 Claims. (Cl. 55-85) This invention relates to an improved method and apparatus for cleaning exhaust gases from oxygen steelmaking furnaces.

In an oxygen steelmaking process, a stream of oxygen contacts molten iron in a furnace and oxidizes various impurities from the iron. The exhaust gases from the furnace are extremely hot and dirty and must be cooled and cleaned before they discharge into the atmosphere, The gases may be cleaned either in a precipitator or by wet-washing. One dithculty encountered in usual wetwashing systems with which I am familiar is that heavy particles recovered from the gases tend to plug parts of the equipment and otherwise interfere with its proper operation. Y

An object of the present invention is to provide an improved method and apparatus, operable in conjunction with an otherwise conventional wet-washing system, for handling and removing heavier particles from the water land preventing their interference with operation of the equipment.

A further object is to provide an improved method and apparatus of the foregoing type in which the heavier particles are retained in a critically designed settling column ahead of the disposal equipment for the lighter particles.

In the drawing:

The single gure is a diagrammatic view of au oxygen steelmaking furnace and wet-washing equipment for the exhaust gases including my improved apparatus for handling the heavier particles.

The drawing shows a conventional oxygen steelmaking furnace 10, a lance 12 for introducing oxygen thereto, and a hood 13 covering the furnace mouth. The furnace contains a charge of molten iron with which the oxygen reacts and causes hot gases (about 3500 F.) to be emitted at high velocity from the mouth into the hood. These gases carry many large and small liquid particles, including iron, slag and various metallic oxides. Most of these particles fall back into the furnace, but as much as about 40 pounds of particles per ton of steel continues on with the gases and must be removed by the gas-cleaning system.

The hot dirty gases leave the hood through a stack 14, which leads to a quench box 15. A fan 16 farther along in the system draws the gases through the stack and quench box and maintains this part of the system under a partial vacuum. Further oxidation takes place in the stack, and the temperature of the gases can reach a maximum of about 4000 F. The quench box contains a spray device 17 which directs water on the gases in sufcient quantity to lower their temperature to about 185 F., and thus solidify all liquid particles therein. The water also wets all the heavier particles and many lighter particles. The wetted particles drop out of the gas stream in the quench box. The water provides a flume of suicient ilow to carry away whatever solid particles drop out of the gas stream.

A conduit 18 carries gases from the quench box 15 Vthrough a venturi washer 19 into a cooling tower 20,

which contains water approximately to the level indicated in the drawing. As the gases leave the quench box, they still carry smaller lighter particles. A pump 21 directs water from the bottom of the cooling tower through a 3 ,3 15,443 Patented Apr. 25, 1967 pipe 22 into the venturi washer 19, where the water co1- lects the particles from the gases. The resulting sludge settles in the bottom of the pool of water in the cooling tower. Another spray device 23 in the top of the cooling tower provides cooling water to lower the vapor content of the gases. The cooling tower is equipped with a sealed overflow 24 and a water-level control 25. Clean gases discharge from the cooling tower through a main 26, which contains the aforementioned fan 16, and out a stack 27 into the atmosphere. The base of stack 27 has a final moisture separator 2 8. Preferably the top of the quench box 15 has 'an emergency stack 29, which normally is closed but can be opened to discharge gases directly from the quench box if the subsequent equipment is not operating.

A pump 32 directs sludge from the bottom of the cooling tower 20 through a pipe 33 into a conventional thickener 34, which has an overliow 35 for discharging excess clear water to the sewer. Underflow from the thickener is handled in a conventional filter-cake machine 36. The latter is connected to the bottom of the thickener via a pipe 37, which contains a pump 3S. The filter-cake machine dewaters the sludge from the thickener and directs it to a load-out hopper 39. A return pipe 40 carries water from the lter-cake machine back to the thickener. Preferably the filter-cake machine operates only intermittently when the sludge becomes sufficiently concentrated that the solids can be removed economically from the system. During periods when the filter-cake machine is out of operation, pump 38 continues to run to prevent plugging of the outlet 'at the base of the thickener.

Water from the quench box 15 discharges into a scupper 41 which is equipped with a scalping screen 42. The screen catches the largest particles and foreign bodies which sometimes drop into the quench box and would plug or damage subsequent equipment. Material caught on the screen discharges through a chute 43 into a load-out hopper 44. Chute 43 is equipped with sealing aps 45. Water and solids which pass through the scalping screen 42 discharges from the scupper 41 through a vertical pipe 46 into a quench-water settling standpipe 47. A pump 48 recirculates the quench water from the standpipe through a pipe 49 to the spray device 17 in the quench box 15. A pipe 50 supplies make-up water to the standpipe from the cooling tower 20.

All the structure and oper-ation thus far described are conventional, and hence are not shown nor described in greater detail. Prior to my invention the practice was to pump water-borne solids directly from the bottom of standpipe 47 to the thickener 34 or to pass these solids through a cyclone between the standpipe and thickener to remove heavier particles. Neither practice was successful, as heavier particles plug the thickener, filter-cake machine, or cyclone. With the cyclone further processing, such as a drag conveyor, is necessary to separate the heavy particles from the carry-over water. The usual practice of operating the filter-cake machine 36 intermittently and the pump 3S continuously is successful in preventing plugging only when the solids in the thickener 34 do not vary greatly in size and specific gravity. In the present application heavier particles segregate at the center of the thickener and at the base of the filter-cake machine and cause an acute plugging problem.

In accordance with my invention, I interpose a heavyparticle separator 52 between the standpipe 47 and the thickener 34. The separator 52 includes a relatively long narrow settling tank 53, to one end of which water-borne solids feed from the standpipe through a pipe 54. Preferably the head of solids and water in the standpipe is suicient to feed these materials into the tank, and the pipe 54 contains a valve 55 only for control purposes. Howmay arise.

ever, I can replace this valve with a pumpif needed. A column 56 extends downwardly from tank 53 spaced from the location `at which the solids enter. The tank is relatively shallow and its bottom slopes downwardly toward the column 56. Heavier particles among the solids drop out of suspension and collect in the column. I mount a rotar] feeder 57 at the bottom of the column to withdraw particles, as hereinafter explained. The feeder directs these particles to another load-out hopper S. The feeder has a drive motor 59. Water and lighter parti-cles overflow from the settling tank into a pipe 60 which carries them to the thickener 34.

The minimum dimensions of the settling tank 53 and Vcoiumn 56 are critical, although of course the optimum dimensions vary indifferent installations where the fiow Vrates and the quantities and characteristics of the solids are diiferent. The tank should provide sufficient yretention time to allow the heavier patricles 'in the suspension to settle into the column. The column should have sucient height that the bed of particles therein does not allow water to pass. In a typical installation where the volume of solids and water is about 300 gallons a minute,

to start the motor and driveV theV feeder 57 to remove parti-y clesA from the bottom. When the Vheight drops to the level of the lower switch 62, the latter switch operates to stop the motor. Typically the upper switch 1 can be 9 feet above the @bottom of the column and the lower switch 62 can be 5 feet thereabove. I have not shown the electrical connections, since they follow well-known principles." Y

Particles'at'the bottom of coltunn 56 of course are wet, but they contain no loose water. The bed of particles in the column forms an effective barrier against leakage of water from tank 53. Particles which remain in the water passing from the tank to the thickener 34 are sufficiently fine and of a character that they do not interfere with proper-operation of the thickener.V

While I have shown and described onlya single embodiment of my'invention, it is apparent that modifications Therefore, I do not Wish to be limited to the disclosure set forth butonly bythe scope of the appended claims. Y Y

.-I claim:

1; In a wet-washing process for cleaning exhaust gases from an oxygen steelmakin-g furnace, which process includes quenching the gases with water to pick up in the water a portion of the particles carried by the gases, which portion includes all the heavier particles along with some lighter particles, transferring the water and particles picked up therein to a standpipe, recovering as a sludge another portion of the particles carried by the gases, which other portion is composed of lighter particles, and thickening said sludge, the combination therewith of a method of handling particles which go into said standpipe, said method comprising transferring water-borne particles from the-bottom of said standpipe to a settling tank, rel taining'rthe water and particles in said tank until the heavier particles settle from the water and lighter particles forming -a column of minimum height of about 4 feet of settled heavier .particles from said tank, withdrawing heavier particles from the ybottom of said column, and thicken- Ving the water and'lighter/particles from said tank to the exclusion of the heavier particles.

2. A meth-od as defined in claim 1 in which particles are withdrawn from the bottom yof said column when the height of the column reaches about 9 feet, and'withdrawal of particles discontinues when the height of the column drops to about 5 feet. Y

3. A method as defined in claim 1 in which the water and particles fromV said standpipe feed to one end of said tank and flow along the length of the tank, and said column extends downwardly at a location spaced from that at which Vthe water and particles feed into the tank.

4. A method as defined in claim 1 in which water and particles picked up therein pass through a scalpingscreen to exclude the largest particles and foreign `bodies from said standpipe.

S. A method as defined in claim'l in which the head Vof water and particles in said standpipe serves Yto Vfeed Y' them into said tank.

6. In a wet-washing system for cleaning exhaust Vgases from an oxygen Vsteelmaking furnace, which system includes means for quenching the gases with water and the-reby picking up in the water a portion of the particles carried by the gases, which portion includes all the go into said standpipe, said apparatus Vcomprising Va` settling' tank, means for transferring water-borne particles from said standpipe to said tank, a column extending downwardly from said tank Vand having a minimum height of about 4 feet, said column receiving heavier particles which settle in said tank, means for withdrawing heavier particles Ifrom the bottom of said column, and means for transferring water and lighter particles from said tank to said thickener to the exclusion of the heavie f particles. Y

7. An apparat-usas dened in claim 6 further compris- Y ing spaced-apart means on said column for Yinitiating withdrawal of particles when the height` ofthe bed-of particles in said column reaches' about 9 feet and discon-. tinuing withdrawal when the height drops to about feet.

8. An apparatus as delined tank is relatively long and narrow, the means for transferring particles to said tank feeds them at one end-thereof, and said column extends downwardly from a location Y Y Y spaced from that at which particles feed'to the tank.-V

9. An apparatus as defined in claim 6 further comprising a scalping screen ahead of said standpipe to exclude the largest particles and foreign bodies fromV said standppe- 1G. An apparatus as defined in claim 6 in which said standpipe provides a head of water and particles for feeding them into said tank.

References Cited by the Examiner UNITED STATES PATENTS -REUBEN FRIEDMAN, Primary Examiner.

J. ADEE, Assistant Examiner.

in `claim 6 in which saidY UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,315,443 April 25, 1967 Jesse D. Marino It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 25, after "minimum" insert` height line 33, for "switch l" read switch 6l Signed and sealed this 14th day of November 1967.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER ttesting Officer Commissioner of Patents 

1. IN A WET-WASHING PROCESS FOR CLEANING EXHAUST GASES FROM AN OXYGEN STEELMAKING FURNACE, WHICH PROCESS INCLUDES QUENCHING THE GASES WITH WATER TO PICK UP IN THE WATER A PORTION OF THE PARTICLES CARRIED BY THE GASES, WHICH PORTION INCLUDES ALL THE HEAVIER PARTICLES ALONG WITH SOME LIGHTER PARTICLES, TRANSFERRING THE WATER AND PARTICLES PICKED UP THEREIN TO A STANDPIPE, RECOVERING AS A SLUDGE ANOTHER PORTION OF THE PARTICLES CARRIED BY THE GASES, WHICH OTHER PORTION IS COMPOSED OF LIGHTER PARTICLES, AND THICKENING SAID SLUDGE, THE COMBINATION THEREWITH OF A METHOD OF HANDLING PARTICLES WHICH GO INTO SAID STANDPIPE, SAID METHOD COMPRISING TRANSFERRING WATER-BORNE PARTICLES FROM THE BOTTOM OF SAID STANDPIPE TO A SETTLING TANK, RE- 